000
FXUS63 KFSD 162347
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
647 PM CDT THU MAY 16 2013

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 324 PM CDT THU MAY 16 2013

FORECAST FOCUS IS ON MCV CURRENTLY PUSHING NE ACROSS THE WESTERN
AND SOUTHERN FORECAST AREA WITH THE CIRCULATION CENTERED NEAR THE
SOUTHWEST CORNER. PROGRESSION HAS BEEN QUICKER THAN PREVIOUSLY
FORECAST AS POTENT UPPER WAVE EJECTS OVER WESTERN NEBRASKA THIS
AFTERNOON PER LATEST WATER VAPOR LOOP. MAIN SURFACE WARM FRONT AND
MOISTURE PUSH HAVE LIFTED NORTH AND ARE APPROACHING THE KSUX TO
KSLB AREA PER UPPER 50S/LOW 60S DEW POINTS AT KTQE AND KDNS.
STRONGER STORMS WILL CONTINUE TO BUILD SOUTH ALONG THE LAGGING
BOUNDARY AND PROGRESS EAST ALONG AND SOUTH OF THIS MOISTURE
BOUNDARY WHERE THE INSTABILITY MAX LIES. THIS INSTABILITY /MUCAPES
OF 1000-1500 J/KG/ WILL CONTINUE TO PUSH NORTH...MAKING SOME
STRONGER STORMS POSSIBLE THROUGH THE NEXT FEW HOURS THROUGH THE
SOUTHERN FA...THROUGH KSUX AND MUCH OF NW IA. WITH INITIAL DRY AIR
IN PLACE NEAR THE SURFACE...STORMS SOUTH ALONG THE LINE HAVE BEEN
PRODUCING SOME STRONG WIND GUSTS LIKELY DUE TO QUICK EVAPORATIVE
COOLING. THERE WAS A GUST TO 50 KT AT KANW AT 1735Z. FARTHER NORTH
WHERE DRY AIR WILL REMAIN IN PLACE LONGER IN THE LOW
LEVELS...STORMS WILL REMAIN MORE ELEVATED...BUT STILL PRODUCE SOME
STRONGER GUSTS TO 40 TO 45 MPH. WARM/UNSTABLE AIR CONTINUES TO
PUSH NORTHWARD TONIGHT /BECOMING A BIT MORE ELEVATED WITH
INVERSION/ HOWEVER MAIN SYNOPTIC FORCING MECHANISM /VORT MAX/ WILL
ALSO PUSH THROUGH. HAVE KEPT POPS LONGER OVERNIGHT BECAUSE THE
AIRMASS IS UNSTABLE...HOWEVER SINCE NO GOOD FORCING
REMAINS...COVERAGE SHOULD BE MINIMAL AFTER THE MAIN WAVE.

UPPER SHORT WAVE WILL MOVE OFF TO THE ENE FRIDAY MORNING...ALTHOUGH
SURFACE BOUNDARY WILL LINGER JUST ALONG THE NORTHERN BORDER OF THE
FORECAST AREA...FROM CHAMBERLAIN...TO HURON...TO MARSHALL AND THEN
TOWARD THE TWIN CITIES. THIS WILL KEEP A RELATIVELY HUMID AIRMASS IN
PLACE WITH DEW POINTS IN THE LOW 60S. NAM SHOWING SOME REDEVELOPMENT
OF CONVECTION ALONG THE BOUNDARY TOMORROW AFTERNOON WITH A WEAK VORT
IN UPPER RIDGING ALOFT...HOWEVER ECMWF/GFS KEEP RIDGING/SUBSIDENCE
DOMINANT. WILL KEEP LOW POPS IN ATTM SINCE AIRMASS IS CONVECTIVELY
UNSTABLE...HOWEVER CONFIDENCE IN REDEVELOPMENT IS LOW ATTM.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 324 PM CDT THU MAY 16 2013

A PRETTY LOW THREAT OF STORMS WILL CONTINUE OVER THE WESTERN EDGE
OF THE FORECAST AREA FRIDAY NIGHT UNTIL MID AFTERNOON SATURDAY AS
CAP QUICKLY BUILDS AND ESTABLISHES ITSELF. THIS CAPPING HAS BEEN
CONSISTENTLY SHOWING IN THE MODEL RUNS FOR THE LAST DAY OR TWO.
INSTABILITY AND MOISTURE WILL STILL BE AROUND THE AREA BUT DYNAMIC
LIFT WILL MOSTLY NOT BE THERE. THIS SETUP WILL ALSO ALLOW FOR SOME
HALF DECENT WARM DAYTIME TEMPERATURES SATURDAY FOR PROBABLY OUR
BEST COMBINATION OF HEAT AND HUMIDITY SO FAR THIS SPRING...THOUGH
MODELS ARE STILL OVERDOING DEW POINTS A LITTLE. EVEN THOSE STORMS
FAR WEST AND NORTH CENTRAL ARE IN SOME QUESTION UNTIL A
COMBINATION OF HEATING AND SOME LIFT WITH APPROACHING TROUGH LATE
SATURDAY AFTERNOON ALLOWS FOR POSSIBLY SEVERE STORMS TO DEVELOP
FROM CENTRAL SOUTH DAKOTA INTO OUR WESTERNMOST AREA SUCH AS HURON
TO CHAMBERLAIN. FORCING CONTINUES TO IMPROVE SATURDAY EVENING AND
THIS SEVERE STORM THREAT WILL SPREAD EAST INTO THE WESTERN HALF OF
THE FORECAST AREA. A TORNADO OR TWO SEEMS POSSIBLE FAR WEST
THROUGH EARLY EVENING WITH THE BEST LOW LEVEL WIND
FIELDS/SHEAR...OTHERWISE THE SEVERE THREAT WILL BE LARGE HAIL AND
LOCALLY DAMAGING WINDS. THE CONFIDENCE OF THIS THREAT IS FAIRLY
HIGH...BUT IT WILL DROP OFF FURTHER EAST THROUGH SATURDAY EVENING
AS DEVELOPING SHOWERS AND STORMS WILL HAVE LESS INSTABILITY AND
WEAKER WIND FIELDS TO WORK WITH. THE SEVERE THREAT WILL CONTINUE
TO DROP OFF WITH TIME LATER SATURDAY NIGHT AS LIKELY WIDESPREAD
PRECIPITATION PUSHES EAST BUT INSTABILITY IS LESS...AND ACTIVITY
PUSHES FURTHER EAST OF THE LOW LEVEL BOUNDARY. RAINFALL POTENTIAL
WILL FOLLOW THE SAME PATTERN WITH OVER AN INCH LIKELY NORTHWEST
SATURDAY NIGHT...TO LESS THAN A QUARTER INCH SOUTHEAST...WITH THE
ABOVE MENTIONED WIDESPREAD RAINFALL LOSING ITS INTENSITY.

SUNDAY WILL BRING THE UPPER SYSTEM MOVING INTO THE AREA...SO THE
THREAT OF NUMEROUS TO WIDESPREAD SHOWERS AND A FEW STORMS WILL
CONTINUE ...BUT THE INSTABILITY AND BEST AVAILABLE MOISTURE WILL
MOVE TO SOUTHEAST OF THE AREA...SO SUNDAY MAY BE WET AND BUSY BUT
NOT TOO EXCITING...AND THE RAINFALL SHOULD NOT BE COPIOUS. TEMPERATURES
OF COURSE WILL NOT BE AS WARM SUNDAY WITH THE GREATER CLOUD COVER
AND RAIN COVERAGE. THIS IS HAPPENING AS THE TROUGH FORMS AN UPPER
LOW OVER THE AREA WHICH ONLY SLOWLY DRIFTS EAST OF THE AREA NEXT
WEEK. SO...THE THREAT OF RAIN SHOULD DECREASE MONDAY THROUGH
WEDNESDAY...THEN WE SHOULD HAVE A DRY DAY NEXT THURSDAY. HOW LONG
BEYOND THE FORECAST PERIOD THE DRY WEATHER LASTS WILL DEPEND ON
THE BEHAVIOR OF THE DEVELOPING MAJOR TROUGH AND RIDGING OVER OUR
AREA EAST OF THE TROUGH. TEMPERATURES TUESDAY THROUGH THURSDAY
LOOK SEASONABLY COOL OVERALL...WITH NIGHTTIME TEMPERATURES COOLING
AND DAYTIME READINGS WARMING DURING THE WEEK AS THE AIR SLOWLY
DRIES OUT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 646 PM CDT THU MAY 16 2013

MOST OF THE ACTIVE WEATHER WILL BE THIS EVENING ACROSS THE AREA.
ONE AREA OF RAIN...WITH EMBEDDED THUNDERSTORMS SOUTH OF HWY 18 IN
NW IA...WILL EXIT THE AREA BY 01Z. HOWEVER ANOTHER LINE OF
CONVECTION HAS DEVELOPED IN CENTRAL NEBRASKA AHEAD OF THE PRIMARY
UPPER LEVEL WAVE. THIS LINE SHOULD ORGANIZE AND EXPAND IN COVERAGE
THROUGH 03Z. EXPECT THE THUNDERSTORMS TO REACH THE MISSOURI RIVER
NEAR YKN BY 01Z AND THEN I-29 FROM KFSD TO KSUX BETWEEN 02Z AND
03Z. WOULD NOT BE SURPRISED TO SEE WIND GUSTS TO 30 OR 35 KTS ON
THE LEADING EDGE OF THE CONVECTION AS HAS BEEN OBSERVED IN CENTRAL
NEBRASKA. BEST CHANCE IS AROUND SUX SO PUT IN TAF THERE. FARTHER
NORTH TOWARD KHON AND KBKX...BELIEVE THE INSTABILITY IS TOO
LIMITED AND THEREFORE KEPT PRECIPITATION OUT OF TAF AS PROBABILITY
IS LESS THAN 50 PERCENT. PRECIPITATION SHOULD MOVE EAST OF AROUND
BY 09Z LEAVING A WARM FRONT NEAR I90. ALONG AND NORTH OF THE
FRONT...EXPECT MVFR CEILINGS. IS NOT OUT OF THE QUESTION THERE
COULD BE IFR CEILINGS OR EVEN SOME LIGHT FOG. DID ADD THE LIGHT
FOG TO KFSD BUT NOT KHON AND FOR NOW PROBABILITY OF IFR CONDITIONS
IS TOO LOW TO ADD TO TAF BUT WILL MONITOR FOR NEXT SET OF
FORECASTS. THE WARM FRONT WILL SLOWLY MOVE NORTH AFTER 12Z...CLEARING
SKIES TO THE SOUTH OF THE BOUNDARY AND SHIFTING WINDS TO 180
DEGREES. WHILE AN ISOLATED STORM IS POSSIBLE NORTH OF THE FRONT
AFTER 21Z FROM KHON TO KMML...DID NOT ADD TO TAF AT THIS TIME DUE
TO THE LOW PROBABILITY OF AFFECTING KHON.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...
LONG TERM...
AVIATION...SCHUMACHER